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Old 20th June 2010, 11:15 PM   #1
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Default transformer identification

Hey all,

So a friend of mine gave me some tube amp parts a few years ago when I thought I would have time to build an amp. School got in the way, yadda yadda. Now I'm ready to start. And I ran into a problem. I can't ID a pair of the transformers my friend gave me and I can't remember if they're output transformers or not.

Both are rather small, 2" long, 1.5" on the coil, and 1.75" high. One side has a green and a black wire coming out and the other side has an orange, a red, a brown, a green/black, and a yellow wire coming out of it. The markings on the side that has the most wires coming out of it are:

320265-3
B-130A28
831841

And that is unfortunately all I've got.

Thanks in advance for any help you guys can give me.

-Elain
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Old 20th June 2010, 11:19 PM   #2
Salas is offline Salas  Greece
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Try a cellphone picture at least, and welcome to the forum.
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Old 21st June 2010, 12:09 AM   #3
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here's an image of the side with the numbers an such... webcam is the only thing I've got.
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Old 21st June 2010, 12:10 AM   #4
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Measure the winding resistances.
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Old 21st June 2010, 12:46 AM   #5
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Resistances measured....

the black and green side has 0.6 ohms
the other side:
yellow and orange is 8.7 ohms
black and brown is 95.2 ohms
black and red is 178.4 ohms
brown and red is 83.3 ohms

Not sure if that is any help...
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Old 21st June 2010, 12:47 AM   #6
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size and leads suggest a small pp u/l OPT. What are the other parts you have?
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Old 21st June 2010, 12:55 AM   #7
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Quote:
Originally Posted by aardvarkash10 View Post
size and leads suggest a small pp u/l OPT. What are the other parts you have?
well, I have a 115 to 115 isolation transformer, a radioshack 6.3-0-6.3 3A transformer, 2 12AX7A, 4 50C5, a 50EH5, a 12AV6, and a pair of 12BA6.

for a different project, a sopht amp that hasn't yet been built because I can't find a 600 ohm to 8 ohm transformer, I have 4 12AE3 and 4 12K5
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Old 21st June 2010, 08:39 AM   #8
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and since the unidentified transformer is small, I would bet it is for a push-pull ECL86 amp (I don't remember the american equivalent). But in any case, it looks way to small to give decent bass, it is old and maybe the laminations have disintegrated, and in general it is likely to disappoint you. I would not use it.
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Old 21st June 2010, 02:51 PM   #9
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There's a few ways to identify the transformer. I would problably use the 6.3v transformer you have ad connect the 6.3v to the black and green with a 1-10 Ohm 5W resistor in series (as a precaution). You should now be able to measure ALL windings and if you are lucky, they are all the relevant voltages (if the the black-green is the 6.3v secondary) and it's the power transformer.

The output transformer usually have more connections to two coils. Here I would take the highest ohmic combination on the secondary (the lowest total resistance of the two coils) and again connect to 6.3v as above, and measure all the voltages between all wires. Take the biggest voltage read on the primary and divide it with the MEASURED voltage you apply (after the resistor), square the result, multiply this with your best guess of the output impedance - result primary impedance. You must figure if this is a likely result - if not, you problably guessed the output impedance wrong. As a rule of thumb, most old output transformers have 4, 8 & 16 ohm as outputs. The voltage of the 4 ohm output will be half of the 16 Ohm output and the 8 Ohm the square root of 2 multiplied with the 4 Ohm output voltage.

It the primary has 3 taps they are anode, HT, anode a Push-Pull transformer - if it has 5 taps they are most likely anode, screen grid, HT, screen grid, anode an Ultra linear Push-Pull transformer.

Hope this helps as a pointer towards identifying your transformers.
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Old 21st June 2010, 03:45 PM   #10
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So I woke up this morning and hooked up one of the transformers as Per B suggested. The thing started smoking soon after. Since both appear to be in the same condition, I'm going to discard them and save up for a nice Hammond output transformer. Thanks for the help though. I'm sure I'll be back soon and often.
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